1. Field of the Invention
The present invention relates to an Amplitude Probability Distribution (hereinafter referred to as an ‘APD’ and also simply referred to as an ‘hour rate’) measurement apparatus for measuring a probability that the size of a frequency component will exceed a predetermined threshold value by analyzing the frequency components of a signal.
2. Discussion of Related Art
An APD measurement technique has conventionally existed. The amplitude of a signal is closely related with the frequency band including the signal. Here, the signal is referred to as an input signal. It is assumed that the frequency component includes frequency band components. There has been known a Fast Fourier Transform (hereinafter referred to as ‘FFT’) type APD measurement apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2008-039762 (hereinafter referred to as ‘Patent Document 1 ’) and a filter bank type APD measurement apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2008-275401 (hereinafter referred to as ‘Patent Document 2 ’). The FFT type APD measurement apparatus is configured to separate an input signal into frequency band components using FFT and extract specific frequency band components from the input signal. The filter bank type APD measurement apparatus includes filters arranged in parallel and configured to extract specific frequency band components from an input signal, and it separates an input signal into frequency band components and extracts specific frequency band components from the input signal.
Meanwhile, with the recent appearance of the Orthogonal Frequency Division Multiplex (OFDM) scheme, the use efficiency of the frequency is increased and multi-channel is in progress. TOSHIBA REVIEW VOL. 58 No. 12 2003, p 2˜6 discloses a description relating to the OFDM scheme (i.e., the standards and the transmission methods for terrestrial digital broadcasting). In the OFDM scheme, digital modulation is performed on transmission data with the transmission data divided into several thousands of low-speed data in a predetermined band. For example, in terrestrial digital broadcasting, a predetermined band is about 5.6 MHz. Thus, digital modulation is performed on transmission data with the transmission data divided into a total of 5,600 carriers, each having about 1 kHz.
As described above, even in the case of, for example, the standard for terrestrial digital broadcasting, in APD measurement in the OFDM scheme, the frequency of a signal must be analyzed using the channel interval of each signal component having about 1 kHz, and the APD of each frequency band component must be measured for several thousands of channel units. Furthermore, the APD measurement apparatus disclosed in Patent Document 2 has been known to perform measurements for a plurality of channels at the same time.